CHAPTER 2 AIRCRAFT SYSTEMS - · PDF fileCHAPTER 2 . AIRCRAFT SYSTEMS . Piper Seneca 1 ....
Transcript of CHAPTER 2 AIRCRAFT SYSTEMS - · PDF fileCHAPTER 2 . AIRCRAFT SYSTEMS . Piper Seneca 1 ....
27
CHAPTER 2
AIRCRAFT SYSTEMS
Piper Seneca 1
ELECTRICAL SYSTEM
The electrical systems in multi engine aircraft are
complicated. It is necessary to understand the electrical
system for the aircraft you intend to fly in order to be
able to cope with a partial or complete electrical failure.
The electrical schematic in Fig. 2.1 is for a
Cessna 421, but it is representative of light to medium
twins. The battery in the center left of the diagram
provides power to the battery bus, which in turn
distributes it to the starters, the avionics bus and the main
bus for the aircraft electrical systems. When the engines
are running, the alternators provide power through the
voltage regulators and overvoltage relay to the battery
bus and to the main bus.
Aircraft Technical Book Company http://www.ACtechbooks.com
28
Electrical Schematic for a C-421
Fig. 2.1
In this aircraft, the avionics bus is normally
powered by the battery through the battery bus. There is
an emergency avionics bus switch that can power the
Aircraft Technical Book Company http://www.ACtechbooks.com
29
avionics bus directly from the main bus. There is also an
emergency alternator field switch that will allow the
alternators to provide power through the battery bus to
the main bus in the event an alternator field circuit
breaker pops.
Fig. 2.1 also shows the external power circuit to
the battery bus. As this circuit does not include the
battery itself, the battery must be left off while the
external power is plugged in or damage to the battery
may result. Some twins require the battery to be “on”
before external power is selected “on”. You must know
which is the case for your aircraft.
Each alternator should be capable of carrying the
entire electrical load. It is wise however, to reduce the
electrical load as much as possible when an alternator
failure occurs to avoid over drawing the remaining
alternator. An ammeter (Fig. 2.2) that shows a discharge
indicates that an alternator is being over drawn or has
failed.
Ammeter Types
Fig. 2.2
Aircraft Technical Book Company http://www.ACtechbooks.com
30
A failed alternator may be reset once. This should
also be carried out under a reduced electrical load. If it
fails to stay on line after one reset, check the alternator
circuit breakers and fuses, and if necessary select the
emergency alternator field switch, if the aircraft has one.
A popped Circuit breaker should only be reset
once. If it pops again, no attempt should be made to reset
it. Continuous resetting of a circuit breaker may start an
electrical fire.
Learn the electrical system for each aircraft you
fly, especially if you plan to fly it IFR.
FUEL SYSTEM
Fuel systems vary considerably between aircraft
types. Piper Seneca aircraft use a simple system where
all of the fuel tanks on one side are interconnected to
function as a single tank.
Older Cessna 421 (Fig. 2.3) aircraft have a much
more complicated system where all take-offs and
landings must be carried out on the main tanks (tip
tanks). Auxiliary or nacelle tanks, if installed, feed into
the tip tanks when the nacelle tank transfer pumps are
selected on, but this transfer should not take place until
the tip tanks are no more than ½ full as the nacelle tanks
feed in faster than the engines use the fuel out of the tips.
The wing tanks can be used after the nacelle tanks. The
wing tanks however, do not have a cross-feed capability.
They should be used immediately after the nacelles have
been used, so that the tip tanks are kept as a reserve in
case of a need to transfer fuel later in the flight.
Aircraft Technical Book Company http://www.ACtechbooks.com
31
C-421 Fuel System Schematic
Fig. 2.3
Aircraft Technical Book Company http://www.ACtechbooks.com